I have narrowed a few things down so far:
It is the cylinder closest to the front which is missing
The plug that came out was black and sooty unlike rest ( I replaced this with a new one )
Replaced the distributor
Tested the leads for spark and are all good

The things I have changed on the Vehicle since I got it:
Swapped airbox for a cone filter with heat shield.
replaced spark plugs with new NGK's ( was Bosch plugs before )
replaced oil ( 10w-40 ) and oil filter

I am thinking of changing the ignition coil next, any ideas what this could be?